The present invention relates to a fuel delivery pipe for supplying fuel supplied from a fuel booster pump of an electronic fuel injection type automotive engine to respective intake passages of the engine through an injector, and is aimed at reducing the radiation noise generated during fuel injection from the injector.
Conventionally, fuel delivery pipes are known in which a plurality of injectors are provided to supply fuel such as gasoline to a plurality of cylinders of the engine. In this fuel delivery pipe, fuel introduced from a fuel tank through underfloor piping is sequentially injected into a plurality of intake pipes or cylinders of the engine from the plurality of injectors, and this fuel is mixed with air. As this air-fuel mixture is burned, an output of the engine is produced.
These fuel delivery pipes include a return type which has a circuit whereby in a case where fuel has been excessively supplied from the fuel tank, that excess fuel is returned to the fuel tank by a pressure regulator, and a returnless type which does not have the circuit for returning the excess fuel to the fuel tank. Recently, returnless type fuel delivery pipes are frequently used for the purposes of cost reduction and the prevention of a temperature rise of the gasoline in the fuel tank.
Since this returnless type fuel delivery pipe does not have the piping for returning the excess fuel to the fuel tank, if the interior of the fuel delivery pipe is decompressed by the fuel injection from the injectors into the intake pipes or cylinders of the engine, pressure waves which occur due to this sharp decompression and the stopping of the fuel injection causes pressure pulsation in the interior of the fuel delivery pipe. After this pressure pulsation is propagated from the fuel delivery pipe and a connection pipe connected to this fuel delivery pipe to the fuel tank side, the pressure pulsation is reversed by a pressure regulation valve in the fuel tank and is returned, and is propagated to the fuel delivery pipe through the connection pipe. The fuel delivery pipe is provided with a plurality of injectors, and the plurality of injectors sequentially effect the injection of fuel and generate pressure pulsation. As a result, this pressure pulsation is propagated to the vehicle compartment as noise through clips retaining the underfloor piping to underneath the floor, and this noise imparts an unpleasant feeling to the driver and passengers.
Conventionally, as methods for controlling drawbacks due to such pressure pulsation, a pulsation damper with a rubber diaphragm incorporated therein is disposed in the returnless type fuel delivery pipe to absorb the generated pressure pulsation energy by this pulsation damper, and the underfloor piping which is laid underneath the floor from the fuel delivery pipe to the fuel tank side is fixed to underneath the floor via vibration absorbing clips. Thus, vibrations generated in the fuel delivery pipe or the underfloor piping up to the tank are absorbed. These methods are relatively effective and have effects in controlling the drawbacks due to the generation of the pressure pulsation.
In addition, fuel delivery pipes having a pulsation absorbing function capable of allowing the fuel delivery pipe to absorb the pressure pulsation have been proposed for the purpose of reducing the pressure pulsation, as in the inventions shown in patent documents 1 to 6. In these fuel delivery pipes having the pulsation absorbing function, a flexible absorbing surface is formed on an outer wall of the fuel delivery pipe, and as the absorbing surface is flexurally deformed by being subjected to the pressure generated in consequence of the fuel injection, the absorbing surface absorbs and reduces the pressure pulsation. It thereby becomes possible to prevent the occurrence of abnormal noise due to the vibration of the fuel delivery pipe and other parts.
However, the pulsation damper and the vibration absorbing clips are expensive, and the number of parts increases, entailing a higher cost. Further, a new problem has occurred in the securing of the installation space. On the other hand, in the conventional techniques shown in patent documents 1 to 6, although there is an effect in absorbing the pressure pulsation, there has been a problem in that there can occur the trouble that noise on the high-frequency side of not less than several kilohertz such as clattering noise is generated when an injector spool is seated onto a valve seat or the like as the injector is opened and closed during the fuel injection, and this noise is amplified by the absorbing surface and is radiated to the outside.
In a patent document 7, to reduce this radiation noise, a method is used in which a bead is provided on a wall surface opposing a wall surface where the injector is disposed, and a circular pipe is joined to the opposing wall surface, thereby increasing the surface rigidity of the opposing wall surface. Since the surface rigidity is thus high, in the case where the pressure pulsation has occurred inside the fuel delivery pipe, the fuel delivery pipe is prevented from being deflected greatly by this pulsation, suppressing the radiation of the high-frequency noise to a low level.
[Patent Document 1] JP-A-2000-329030
[Patent Document 2] JP-A-2000-320422
[Patent Document 3] JP-A-2000-329031
[Patent Document 4] JP-A-Hei11-37380
[Patent Document 5] JP-A-Hei11-2164
[Patent Document 6] JP-A-Sho60-240867
[Patent Document 7] JP-A-Hei10-331743
However, according to the method in which a bead is provided on the wall surface, it is technically difficult to make adjustment such that the high-frequency side noise will not be radiated while being provided with the flexibility capable of suppressing the pressure pulsation of a fluid. In addition, if a circular pipe is joined to the flat wall surface, the mutual contact becomes linear contact, and joining stability is insufficient, so that there has been a possibility that the high-frequency noise reverberates inside the circular pipe.